fixes for gcc 4.8 -fsanitize=address

fulltext search was initialized for all MATCH ... AGAINST items
at the end of the JOIN::optimize(). But since 5.3 derived tables
are initialized lazily on first use, very late in the sub_select().

Skip Item_func_match::init_search initialization if the corresponding
table isn't open yet; repeat fulltext initialization for all
not-yet-initialized MATCH ... AGAINST items after creating derived tables.

currently get_mm_tree skipped the evaluation of this constant
and icorrectly proceeded. The correct behavior is to return a
NULL subtree, according to the IF branch being fixed - when it
evaluates the constant it returns a value, and doesn't continue
further.

- Let index_merge allocate table handlers on quick select's MEM_ROOT,
  not on statement's MEM_ROOT. 
  This is crucial for big "range checked for each record" queries, where 
  index_merge can be created and deleted many times during query exection. 
  We should not make O(#rows) allocations on statement's MEM_ROOT.

- When converting a subquery to a semi-join, propagate OPTION_SCHEMA_TABLE.

          The get_mbr() method shouldn't return the error, rather an invalid MBR
          in this case.

Fixed printing column_get finction.

In some cases, when using views the optimizer incorrectly determined
possible join orders for queries with nested outer and inner joins.
This could lead to invalid execution plans for such queries.

        The Geometry::get_mbr() function can return an error on
        a bad data. We have to check for that and act respectively.

- Set MI_INFO::external_ref for MyISAM tables that are parts of myisamMRG table.

./mtr --suite=main,plugins
will work on all branches.

MDEV-4293 Valgrind warnings (Conditional jump or move depends on uninitialised value) in remove_eq_conds on time functions with NULL argument

val_int() is expected to return 0 for NULL's

        Need to check if the number of points is 0 for the polygon.

        Forgotten DBUG_ASSERT should be replaced with the 'return error'.

Item_default_value inherited form Item_field so should create temporary table field similary.

    Additional fixes for possible overflows in length-related
    calculations in 'spatial' implementations.
    Checks added to the ::get_data_size() methods.
    max_n_points decreased to occupy less 2G size. An
    object of that size is practically inoperable anyway.

Item_func_make_set wasn't taking into account the first argument when
calculating maybe_null.

sql/item_strfunc.cc:
  rewrite Item_func_make_set, removing separate storage of the first argument
sql/item_strfunc.h:
  rewrite Item_func_make_set, removing separate storage of the first argument

  
with decimals=NOT_FIXED_DEC it is possible to have 'decimals' larger
than 'max_length', it's not an error for temporal functions.
  
But when Item_func_numhybrid converts the value to DECIMAL_RESULT,
it must limit 'decimals' to be a valid scale of a decimal number.

AVG() returns a double, its max_length is reasonably
limited by a double number length, even if the argument
is many Kbytes long.

MDEV-4281 Assertion `maybe_null && item->null_value' fails in make_sortkey on CASE with different return types, GROUP_CONCAT, GROUP BY

Fix Item::get_date() to mark the item NULL when returning an error.

      The bug was found by Alyssa Milburn.
      If the number of points of a geometry feature read from
      binary representation is greater than 0x10000000, then
      the (uint32) (num_points * 16) will cut the higher byte,
      which leads to various errors.
      Fixed by additional check if (num_points > max_n_points).

This is a bug in the legacy code. It did not manifest itself because
it was masked by other bugs that were fixed by the patches for
mdev-4172 and mdev-4177.

Field_enum incorrectly inherited decimals() from Field_string.
Field_enum should be always integer in numeric context.

Do not include BLOB fields into the key to access the temporary
table created for a materialized view/derived table.
BLOB components are not allowed in keys. 

MySQL Bug #12408412: GROUP_CONCAT + ORDER BY + INPUT/OUTPUT SAME USER VARIABLE = CRASH
and
MySQL Bug#14664077 SEVERE PERFORMANCE DEGRADATION IN SOME CASES WHEN USER VARIABLES ARE USED


sql/item_func.cc:
  don't use anything from Item_func_set_user_var::fix_fields()
  in Item_func_set_user_var::save_item_result()
sql/sql_class.cc:
  Call suv->save_item_result(item) *before* doing suv->fix_fields(), because
  the former evaluates the item (and caches its value), while the latter marks
  the user variable as non-const. The problem is that the item was fix_field'ed
  when the user variable was const, and it doesn't expect it to change to non-const
  in the middle of the execution.

mysys/errors.c:
  revert upstream's fix. use a much simpler one
mysys/my_write.c:
  revert upstream's fix. use a simpler one
sql/item_xmlfunc.cc:
  useless, but ok
sql/mysqld.cc:
  simplify upstream's fix
storage/heap/hp_delete.c:
  remove upstream's fix.
  we'll use a much less expensive approach.

The function remove_eq_cond removes the parts of a disjunction
for which it has been proved that they are always true. In the
result of this removal the disjunction may be converted into a 
formula without OR that must be merged into the the AND formula
that contains the disjunction.
The merging of two AND conditions must take into account the
multiple equalities that may be part of each of them.
These multiple equality must be merged and become part of the
and object built as the result of the merge of the AND conditions.
Erroneously the function remove_eq_cond lacked the code that 
would merge multiple equalities of the merged AND conditions.
This could lead to confusing situations when at the same AND 
level there were two multiple equalities with common members
and the list of equal items contained only some of these 
multiple equalities.
This, in its turn, could lead to an incorrect work of the
function substitute_for_best_equal_field when it tried to optimize
ref accesses. This resulted in forming invalid TABLE_REF objects
that were used to build look-up keys when materialized subqueries
were exploited.